Scrap rubber reclaiming

Addition of scrap rubber in the form of either ground waste vulcanizates or reclaim in rubber compounds gives economic as well as processing advantages. In addition to lowering the cost of rubber compounds, the use of cross-linked rubber particles has beneficial effects such as faster extrusion rate, reduced die swell, and better molding characteristics. 

Le Beau, D.S., Basic reactions occurring during rubber reclaiming. II. The influence of solvent naphtha, storage of reclaim and aging of scrap prior to reclaiming, and infrared spectra of natural rubber reclaim. Rubber Chem. TechnoL, 22, 560, 1949. 

In the Tirecycle process, first developed in 1982, finely ground scrap rubber is treated with a liquid polymer to form a reclaimed rubber product. RRE literature claims superior bonding properties and suggests use in tread rubber and other products including washers, mats, car parts, and tiedowns. The Tirecycle product is claimed to be useful with thermoplastics such as polypropylene, polyethylene, and polystyrene, as well as polyvinyl chloride, polyesters, and urethanes. 

A biotechnological process was developed by Straube et al. for the devulcanization of scrap rubber by holding the comminuted scrap rubber in a bacterial suspension of chemolithotropic microorganisms with a supply of air until elemental sulfur or sulfuric acid is separated. This seems to be an interesting process, which obtains reclaim rubber and sulfur in a simplified manner. 

Up to the time of World War 11, scrap tires contained only natural rubber. Reclaiming processes were well established, and a reasonable proportion (20%) of reclaim was accepted in compounding of new tires. (Frequently, the percentage was much more in other rubber products.) In 1941 the consumption of reclaim was 32% of the consumption of new rubber. 

A few examples of reclaim process of scrap rubber are briefly described. However important they may be for either the quality of the process or for the amount of rubber reused, they should not be considered as a limitation in the possibilities. 

When it comes to finding more complex systems of reusing the scrap rubber powder, recovery alternatives include pyrolysis, gasification, tire derived fuel, reuse and recycling, rubber reclaim, and retreading [3]. 

As already said in the Preface, a question arose as to the appropriateness of having a chapter in this book devoted to the cure of rubbers and to their properties concerned with the recovery of scrap rubber obtained from old tires. However, the amount of old tire rubber is so large that it could be considered as a raw material, and reclaiming will become a necessity when crude oil and natural rubber experience shortages. This problem is so vast that only a book in itself could describe all the possibilities of reusing. Nevertheless, a large number of opportunities has been identified, and the reclaiming processes based on the cure of these scrap rubbers have been considered. 

Butyl and NR tubes and other fiber-free scrap rubbers are reclaimed by means of the heater or pan process. Brass tube fittings and other metal are removed from the scrap. The scrap is mechanically ground, mixed with reclaiming agents, loaded into pans or devulcanizing boats, and autoclaved at steam pressures of 10-14 atm (1.03-1.40 MPa) for 3-8 h. The reclaim is finally processed much the same way as... 

The reclaiming oils and chemicals are complex wood and petroleum derivatives that swell the rubber and provide access for breaking the rubber bonds with heat, pressure, chemicals, and mechanical shearing. Approximately 2—4 parts of oil are used per 100 parts of scrap rubber. Some examples of reclaiming oils include monocyclic and mixed terpenes, i.e., pine-tar products, saturated polymerized petroleum hydrocarbons, aryl disulfides in petroleum oil, cycloparafinic hydrocarbons, and alkyl aryl polyether alcohols. 

There are certain technical limitations in the devulcanization of rubbers, and vulcanization is, in fact, not truly reversible (Pryweller, 1999). The partial devulcanization of scrap rubber will result in a degradation of physical properties. In many cases, this may limit the amount of substitution levels in high-tech applications such as passenger tires. But it can provide the compounder of less stringent products with an excellent low-cost rubber that can be used as the prime rubber or at very high substitution levels. According to Franta (1989), reclaim cannot be used for tread compounds in tires because every addition may decrease their resistance to wear. However, this statement has not been checked in case rubber devulcanized without an addition of chemicals. Considerable amounts of reclaim are consumed for carcasses of bias ply tires for cars if the compounds are of NR for carcasses of radial tires no reclaim is added. On the other hand, reclaim is added to compounds for bead wires and it may also be added to sidewalls. Within the framework of direct recycling options a number of applications for GRT outside the rubber industry have been proposed. Such applications include the use as a tiller in asphalt for the surface treatment of roads and as a rubberized surface for sport facilities. 

CAS 27080-90-6 EINECS/ELINCS 248-212-4 Empirical C16H18S2 Properties M.w. 274.44 Toxicology TSCA listed Uses Reclaiming agent for scrap rubber Manuf./Distrib. A.H. Marks http //WWW. ah marks, com Trade Name Synonyms Aktiplast 6 N [Rhein Chemie http //www.rheinchemie.com]... 

There are certain technical limitations in the devulcanization of rubbers, and vulcanization is, in fact, not truly reversible [11]. The partial devulcaniza-tion of scrap rubber will result in a degradation of physical properties. In many cases, this may limit the amount of substitution levels in high-tech applications such as passenger tires. But it can provide the compounder of less stringent products with an excellent low-cost rubber that can be used as the prime rubber or at very high substitution levels. According to Franta [12], reclaim... 

Reclaim Rubber. Rubber recovered from scrap rubber goods, primarily by digestion or mastication at elevated temperatures, consists of soluble hydrocarbon, crosslinked rubber, and about 30% carbon black, plus minor amounts of oil, tackifiers, and curative residues. The rubber content of reclaim derived from tires is a mixture of SBR and NR, while butyl reclaim is derived from inner tubes. One of the principal virtues of reclaim is price. It is used for black friction tape but to a larger extent for duct tapes and pipe wrap tapes. 

A term which generally applies to vulcanised rubber unfit for any other use than reclaiming or grinding to crumb rubber. In the rubber factory scrap may also refer to unvulcanised trimmings which can be reprocessed. 

For some applications, such as when it is necessary to dissolve or solvate rubbers, or rubber compounds to form doughs and solutions it is desirable to use a machine in this category. Various types of machines can be used to produce the required form. Grinders are also used to reduce scrap vulcanisate to form a rubber crumb for purposes of working this waste product back into cheap compounds, or prior to reclaiming rubber by chemical processes. 

RECLAIMING. Recovery and reuse of scrap materials, either in low percentage in new product manufacture or in larger proportions in products in which the highest quality is nut essential. Among the materials widely reclaimed in industry are aluminum, steel, paper, rubber, glass, crankcase... 

An efficient method of reclaiming vulcanized scrap was developed about 1900, involving digestion of the scrap with NaOH plus a hydrocarbon softener. This separated the cotton insertions from the rubber and partially reversed the effect of vulcanization. Use of reclaim has long been an important adjunct to the industry, especially for low-cost, high-volume products. 

The number of scrap tires in Japan in 1977 was estimated to be approximately h J million with a total weight of 550 thousand tons. Although some of them are reused as reclaimed rubber, recapped tires, etc., it is difficult to recycle all of the scrap tires by the usual methods, therefore, there is a demand for new recycling systems for scrap tires. 

A review of the science and technology of reclaimed rubber was published by Le Beau in 1967. " Knorr has shown the action of diaryl disulfide on the natural and synthetic rubber scraps of technical goods. ... 

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